The present invention relates to admixtures for mineral binders based on hydrogenated disaccharide(s). It also relates to admixture-containing mineral binders and to a process for the preparation thereof.
The term xe2x80x9cmineral binderxe2x80x9d means primarily any hydraulic binder and more particularly any composition, notably any mineral powder, capable of forming with water a paste which sets and hardens gradually, even away from the air. Conventionally, at ambient temperature, a hydraulic binder starts to form such a paste with water within a period of about a few minutes to less than 48 hours, generally between about 30 minutes and 24 hours.
This definition applies to the following, this list being in no way restrictive:
cements, and particularly those belonging to the group comprising cements of the artificial Portland type, cements of the blended Portland type, blastfurnace slag cements, Portland blastfurnace cement 85, Portland pulverized fuel ash cements, and ground cements for more particular uses of the type including slag cement containing lime, masonry cement, natural cement, supersulfated cement, rapid-hardening cement, quick-setting and rapid-hardening cement, cement for work in water with low or high sulfate contents,
natural or artificial hydraulic limes,
mixtures such as mortars, slurries, coatings and concretes based on cement and/or lime, water and/or aggregates of all particle sizes (sands, gravels, crushed stones . . . ) and particularly those belonging to the group comprising ready-mixed dry industrial mortars, site-mixed mortars, pre-batched dry industrial mortars, ready-mixed mortars, grouting compounds, injection mortars, slurries and injection slurries, reinforced and unreinforced concretes, ready-mixed concretes, flowing concretes, heavy concretes, lightweight concretes, lightweight insulating concretes, cellular concretes, fiber concretes, prestressed concretes and fair-faced concretes.
This definition also includes the raw materials used in the production of cements such as pozzolanas, clinkers, slags, calcareous fillers and silica fume.
The term xe2x80x9cmineral binderxe2x80x9d also means non-hydraulic binders, particularly materials based on calcium sulfate, gypsum and/or lime.
Mineral binders are materials which are very widely used, particularly in the building industry, for producing the various parts of structures such as the framework, floor, shell and roof, and also in public works, particularly for the production of bridges, tunnels, dams, roads and other works such as, for example, offshore structures or nuclear power stations.
Depending on the final use of these materials and also depending on the conditions under which they will be used, it is sometimes necessary to add admixtures to the mineral binders. Said admixtures modify, by improving them, the properties of the mineral binders to which they are added in small proportions, generally at most equal to 5% by weight of the mineral binder. Examples of admixtures include grinding agents or grinding auxiliaries, plasticizers, water-reducing plasticizers, superplasticizers, set and hardening accelerators, retarders, air entraining agents, waterproofing compounds and curing agents. These admixtures make it possible, for example, to modify the workability, setting, hardening, strength, durability and/or certain other properties of the hydraulic binder.
Numerous water-reducing plasticizer products or superplasticizers are already in use. Examples include:
molasses derived from sugar beet and sugar cane, which are relatively inexpensive products capable of fermenting and with limited effectiveness;
raw lignosulfonates derived from the paper industry which are relatively inexpensive but have the disadvantage of causing foaming of the mortars or concretes, thus reducing their strength at 28 days;
sugars derived from starch which are good water-reducing plasticizers but strong retarders;
oxidized sugars such as gluconates and oxidized starch hydrolysates which are very good water-reducing plasticizers, retarders and which also make it possible to improve the strength at 28 days as described in French patent FR 2 387 194 and in GB 1 508 761;
sulfonated condensates of naphthalene formaldehyde and sulfonated condensates of melamine formaldehyde which are very good plasticizers, weak retarders but which do not improve the strength at 28 days and are rather unacceptable environmentally;
polyacrylates which are superplasticizers, weak retarders but which bring about little or no improvement in the strength at 28 days;
polyols such as hydrogenated sugars such as sorbitol and hydrogenated starch hydrolysates which, as described in patent FR 2 726 550, are water-reducing plasticizers but which have a markedly weaker retarding effect than oxidized sugars whilst improving the strength at 28 days, as follows from American patent U.S. Pat. No. 4,073,658; hydrogenated sugar syrups are also described as grinding agents, such as oxidized glucose syrups, according to patent EP 0 695 557;
copolymers of styrene and maleic anhydride which are both superplasticizers and grinding agents as follows from patent FR 2 744 714.
At present, for the preparation of cements, the trend is to use products that are less expensive than clinker. However, clinker confers good strength at 28 days. There is a need, therefore, for an admixture capable of correcting the strength at 28 days of cements containing little or no clinker.
Moreover, with regard to mortars, slurries and concretes, industry is seeking plasticizers and water-reducing agents or superplasticizers which are ecologically acceptable and which at the same time confer very good plasticity with little retardation, an early strength i.e. at between 8 and 24 hours, sufficient to allow rapid dismantling of the formwork, and improved strength at 28 days, if possible.
There is a need, therefore, for an ecologically acceptable admixture which makes it possible to obtain a good compromise between retardation, plasticity, early mechanical strength and mechanical strength at 28 days.
Within the scope of the present invention, the term plasticity of the mineral binder means the ability to obtain a Theological state in which the mineral binder is workable, pourable or pumpable.
The plasticity is measured according to the standardized method CEN 196-01 by which the spreading of a given volume of mineral binder over a vibrating table is measured in mm.
The initial set and final set are measured on a mineral binder by means of an automatic setometer with the brand name xe2x80x9cACMELxe2x80x9d.
Within the scope of the invention, the early mechanical strength is measured on a specimen of mineral binder according to the standard CEN 196-01 mentioned above, 17 or 24 hours after the production of said specimen.
For applications in the building sector, this early mechanical strength must generally be more than 5 MPa to allow dismantling of formwork.
Moreover, the strength at 28 days of mineral binders is also measured according to the above-mentioned standard CEN 196-01.
After numerous searches, the Applicants discovered, to their merit, that of all the polyols, only the compositions containing at least 40% by weight of hydrogenated disaccharide made it possible to obtain a good compromise between retardation, plasticity, early mechanical strength and mechanical strength at 28 days. In particular, the Applicants observed, surprisingly and unexpectedly, that the higher the molecular weight of the polyols, the greater their retarding properties, and the lower their molecular weight the greater their tendency to give rise to false sets.
The present invention relates, therefore, to an admixture for mineral binders comprising a polyol composition containing at least 40% by weight, preferably at least 55% by weight and even more preferably at least 65% by weight of hydrogenated disaccharide, this percentage being expressed with respect to the dry weight of all the polyols contained in said composition.
The term xe2x80x9chydrogenated disaccharidexe2x80x9d within the meaning of the present invention means, in particular, a product chosen from the group comprising maltitol, lactitol, glucosido-1,6 mannitol, isomaltitol, cellobiitol, and any mixtures of at least any two of these products such as, for example, palatinitol.
Preferably, the hydrogenated disaccharide is chosen from maltitol, lactitol and any mixtures thereof. Particularly advantageously, the hydrogenated disaccharide is composed of maltitol.
The polyols other than hydrogenated disaccharides that may be contained in said polyol composition may be of very different types and concentrations. They may be products such as sorbitol, mannitol, xylitol, arabitol, iditol, maltotriitol, erythritol, glycerol, hydrogenated oligo- and polysaccharides.
Consequently, the polyol composition which is useful as an admixture for hydraulic binders according to the invention may be composed of, for example:
pure maltitol, or
pure lactitol, or
any mixture of maltitol/lactitol, or
a maltitol syrup or a hydrogenated starch hydrolysate of which the maltitol concentration is at least equal to 40%, or
a mixture based on maltitol and/or lactitol on the one hand and glycerol on the other hand, the hydrogenated disaccharide(s) concentration of said mixture being at least 40%,
a maltitol syrup containing borate such as BOROSORB(copyright) 553 sold by the Applicants.
Said polyol composition may be in the liquid, pasty or solid form, including powders. Any hydrogenated disaccharide that it contains may be crystalline or non-crystalline.
The admixture according to the invention may be entirely composed of the polyol composition as described. It may also comprise, apart from said polyol composition, at least one conventional admixture for mineral binder chosen, for example, from phosphates, sulfates, borates, amines (particularly triethanolamine), calcium salts (particularly calcium chlorides, hydroxides and formates), sulfonated melamine derivatives, sulfonated naphthalene derivatives, polyacrylates, glycols and/or lignosulfonates or mixtures thereof.
The conventional admixtures such as borates, sulfates or phosphates may be introduced in the admixture according to the invention in a quantity of 0.1% to 20%, this percentage being expressed in dry weight with respect to the dry weight of the polyol composition contained in said admixture.
In particular, the Applicants found, surprisingly, that the combination of such a polyol composition, notably maltitol, with certain conventional plasticizers or superplasticizers such as, in particular, lignosulfonates with or without sugar, made it possible to obtain synergistic effects, particularly in terms of mechanical strength of the mineral binders, both in terms of the early strength and the strength at 28 days.
Consequently, the admixture for mineral binders according to the invention may be characterized by the fact that it comprises, apart from a polyol composition as defined above, lignosulfonates with or without sugar, the weight ratio between the lignosulfonates and the polyol composition, expressed in dry weight of lignosulfonates with respect to the dry weight of the polyol composition, being in the range 1/20 to 20/1, preferably in the range 1/9 to 9/1 and even more preferably in the range 1/9 to 1/3.
The admixture according to the invention may itself be in the liquid, pasty or solid form, including powders. It is entirely suitable for use as an admixture for cement before, during and/or after grinding of said cement, as described for example in patent FR 2 744 714 mentioned above, or as an admixture for hydraulic limes. It is also perfectly suitable for use as an admixture for concretes, slurries and mortars whether liquid or solid.
The level of introduction of the admixture according to the invention will depend, inter alia, on the nature, the intended use and the conditions of use of the mineral binder.
In practice, this level will be in the range 0.001% to 5% expressed in dry weight of admixture with respect to the total dry weight of raw material(s) for cement, cement, and/or chalk contained in the hydraulic binder.
The invention also relates to a mineral binder:
chosen from ground or unground cements, raw materials for the production of cements before grinding, hydraulic limes and mixtures thereof, and
that contains 0.001% to 1.5% by weight, preferably 0.005% to 0.5% by weight and even more preferably 0.01% to 0.3% by weight of an admixture as claimed, this percentage being expressed in dry/dry as described above.
According to another variant, the invention relates to a mineral binder:
chosen from mortars, slurries and concretes in liquid, pasty or solid form, and
that contains 0.005% to 5% by weight, preferably 0.01% to 2% by weight and even more preferably 0.02% to 1% by weight of an admixture as claimed, this percentage being expressed in dry/dry as described above.
In a general manner, the admixture according to the invention may be introduced into the mineral binders in a great number of ways. In particular, it may be introduced entirely during a particular stage of production, storage, admixing, hydration, transport or placing of the mineral binder. It may also be introduced in a partial manner during several of these particular stages.
It may, for example, be used wholly or partly during the production of mineral binders in powder form, including production in the cement works themselves before, during and/or after grinding of the cement, or during the preparation of dry and/or ready-mixed mortars or concretes. It may also be used wholly or partly during the transport of non-powder i.e. pasty or liquid mineral binders, or during their production in the works or on site, and for example, in the water and/or aggregates required for the preparation, particularly in vessels known commonly as xe2x80x9cready-mix plantsxe2x80x9d, of mortars, slurries or concretes, or just before the pouring thereof.
The present invention also relates, therefore to a process for the preparation of a mineral binder, in which an admixture as claimed is added in one or more operations to a mineral binder in powder form chosen from the group comprising ground or non-ground cements, raw materials for the production of cements before grinding, hydraulic limes, dry and/or ready-mixed mortars and concretes and mixtures thereof.
According to another variant, the present invention relates to a process for the preparation of mineral binder, in which an admixture as claimed is added in one or more operations a) to a non-powder, particularly pasty or liquid mineral binder chosen from the group comprising mortars, slurries and concretes and/or b) to the water and/or aggregates required for the preparation of said non-powder mineral binder.
Consequently, a general, novel and inventive means is henceforth available for admixing with mineral binders of all kinds, said means being composed of selected polyol compositions, as described above.
The general concept of the present invention is also based on the use of a hydrogenated disaccharide, particularly maltitol, for admixing with mineral binders, particularly with a view to improving the plasticity and/or mechanical properties thereof.
The present invention will be described in more detail with the aid of the examples that follow and which are in no way limiting on the invention.
In all the examples that follow, the spreading measurements (in mm) and mechanical strength measurements (in MPa) at 17 hours, 24 hours or 28 days were carried out according to the standard CEN 196-01.